I believe we should use Mirek's command receiver on L band as adapted for our purposes. If we want a redundant one for any reason, we do that one on 70cm. The command receiver should feed the IHU-3 SDR for any normal commanding and any reset vector decoder we choose to enable. The issue is straightforward. Any module that needs a heat sink will have been designed to be kept cool when the spacecraft is receiving a large thermal input from the sun. When this thermal input is removed, the same radiation cooling that was keeping the module cool will continue to operate irrespective of the solar input. That module will get cold over time. If the bottom temperature stops the unit from operating properly and it is a command receiver, this is not a good thing. I believe we should have dedicated command receivers anyway and these to do not need 80 dB of dynamic range and can be made narrow band. Our solar eclipse pattern has been given a preliminary analysis for the proposed orbit and we will be subjected to eclipses of insufficient duration to cause us severe thermal problems but what thermal issues there are need to be understood and this is what Dick is warning us about. This analysis of the eclipse pattern was also the basis of my analysis that it would take well over a decade to subject any Li-ion battery to sufficient cycles to worry about. Bob N4HY John B. Stephensen wrote:The SAW filters work down to -35 C and the ICs to -40 C so its not too far off. It's easy to use a lower power RF amplifier and mixer which will lower the input intercept. Right now, the receiver is designed to tolerate direct hits from PAVE PAWS at any two frequencies outside the IF passband. As the input intecept is lowered, the percentage of pulses that cause interference increases, but the receiver won't go completely deaf as was reported on earlier satelites. 73, John KD6OZH ----- Original Message ----- *From:* Dick Jansson-rr <mailto:rjansson@cfl.rr.com> *To:* AMSAT Eagle <mailto:eagle@amsat.org> *Sent:* Wednesday, October 11, 2006 17:51 UTC *Subject:* [eagle] Module Temperatures Last evening I tried to convey the concept that the critical-command modules needed to be of low-power design to insure their operability during the occasional rather lengthy eclipse cooling of the spacecraft. My message apparently did not sink in. John reports that his design of such a U band receiver would be dissipating some 3.5W due to its bullet-proof nature against 3rd-order IM products needed for protection on the U band. If we go forward with such a module of that nature, it will need to have thermal control tapes on it to provide a mean emittance of about e=0.45. In a 3 hour eclipse we can expect to see spaceframe temperatures down to -100°C (173K) or lower. With such an environment John's module would be expected to see temperatures down to at least -44°C, which is a bit frosty for electronics that are expected to provide the critical services of commanding the spacecraft. Such operating temperatures are not felt to be advisable for that service. If John's module were of the 1W category, temperatures of the receiver could be expected to be in the range of -15°C to -20°C which would be more operable for the service. The above numbers are, of course, based on estimates which will be confirmed after we have the new spaceframe fully designed and analyzed. The "warmer" temperatures of the lower power modules are those that have been experienced and measured by telemetry from AO-10 and AO-13. These projections are thus based on 25 years of experience in these design concepts. /Dick Jansson/ _---------------------------_ rjansson@cfl.rr.com <mailto:rjansson@cfl.rr.com> _---------------------------_ ------------------------------------------------------------------------ _______________________________________________ Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle ------------------------------------------------------------------------ _______________________________________________ Via the Eagle mailing list courtesy of AMSAT-NA Eagle@amsat.org http://amsat.org/mailman/listinfo/eagle